This invention relates generally to magnetoresistive read heads. More particularly, it relates to magnetoresistive read heads having in-stack longitudinal bias structures.
Thin film magnetoresistive (MR) sensors or heads have been used in magnetic data storage devices for several years. Physically distinct forms of magnetoresistance such as anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR) and spin tunneling magnetoresistance (TMR) are well known in the art. Magnetic readback sensor designs have been built using these principles and other effects to produce devices capable of reading high density data. In particular, three general types of magnetic read heads or magnetic readback sensors have been developed: the anisotropic magnetoresistive (AMR) sensor, the giant magnetoresistive (GMR) sensor or GMR spin valve, and the magnetic tunnel junction (MTJ) sensor.
A magnetoresistive (MR) read head typically includes a top and bottom shield layers, top and bottom gap layers, a read sensor, such as a spin valve, and the first and second leads that are connected to the read sensor for conducting a sense current through the read sensor. The top and bottom gap layers are located between the top and bottom shield layers, and the read sensor and the first and second leads are located between the top and bottom gap layers. Accordingly, the top and bottom gap layers are constructed as thin as possible without shorting the top and bottom shield layers to the read sensor and the first and second leads.
The first and second leads abut the first and second side edges of the read sensor in a connection referred to in the art as a contiguous junction. A spin valve read sensor typically includes a spacer layer sandwiched between a free layer and a pinned layer, and a pinning layer adjacent to the pinned layer for pinning the magnetic moment of the pinned layer. The free layer has a magnetic moment that is free to rotate relative to the fixed magnetic moment of the pinned layer in the presence of an applied magnetic field.
Typically, magnetic spins of the free layer are unstable in small sensor geometries and produce magnetic noise in response to magnetic fields. Therefore, the free layer must be stabilized by longitudinal biasing so that the magnetic spins of the free layer are in a single domain configuration.
There are two stabilization schemes for longitudinal biasing of the free layer. One stabilization scheme is to provide a longitudinal bias field from the lead regions at the side edges of the read sensor. The most common technique of the prior art includes the fabrication of tail stabilization at the physical track edges of the sensor. The efficacy of the method of stabilization depends critically on the precise details of the tail stabilization, which is difficult to accurately control using present fabrication methods.
The other stabilization scheme is to provide an in-stack longitudinal bias structure including a soft ferromagnetic bias layer and an anti-ferromagnetic (AFM) bias layer. FIG. 1 shows an in-stack bias scheme for stabilizing a spin valve of the prior art. A MR sensing head 100 includes a spin valve 102 and an in-stack longitudinal bias structure 104. The spin valve 102 includes a free layer 112, a pinned layer 108, a spacer layer 110 located between the free layer 112 and the pinned layer 108, and an AFM layer 106 adjacent to the pinned layer 108. The in-stack longitudinal bias structure 104 includes a ferromagnetic bias layer 116 and an AFM bias layer 118. The MR sensing head also includes a non-magnetic spacer layer 114 disposed between the spin valve 102 and the in-stack longitudinal bias structure 104. The ferromagnetic bias layer 116 and the AFM bias layer 118 exchange couple to each other, resulting in dominant edge magnetostatic coupling field that stabilize the magnetization of the free layer 112. However, in the prior art in-stack bias scheme, the sense current will be shunted by the bias stack. In addition, the prior art in-stack bias scheme utilizes mainly the edge magnetostatic coupling field that requires self-aligned edges to produce a maximum edge magnetostatic coupling field that is opposite to the interlayer magnetostatic coupling field. It implies a requirement of minimizing the positive interlayer magnetostatic coupling field in order to maximize the longitudinal bias field.
U.S. Pat. No. 6,023,395 issued Feb. 8, 2000 to Dill et al. discloses a magnetic tunnel junction (MTJ) magnetoresistive (MR) read head with an in-stack biasing scheme. The MTJ head includes a MTJ stack, which contains a pinned layer, a free layer and an insulating tunnel barrier layer between the pinned layer and the free layer, a biasing ferromagnetic layer and a non-magnetic electrically conductive spacer layer separating the biasing ferromagnetic layer from the layers in the MTJ stack. The biasing ferromagnetic layer is magnetostatically coupled with the free layer to provide either longitudinal bias or transverse bias or a combination of longitudinal and transverse bias fields to the free layer. However, the in-stack biasing scheme of Dill is not optimal for a spin valve sensor read head since the read current and readback signal will be shunted by the biasing ferromagnetic layer.
There is a need, therefore, for an improved MR sensing head having a spin valve with a magnetically stabilized free layer and without significant shunting of the sense current by the longitudinal bias stack.
A magnetoresistive (MR) sensing head according to a first embodiment of the present invention includes a current-in-plane CIP) sensor, an in-stack longitudinal bias structure, and an electrically insulating layer separating the CIP sensor and the in-stack longitudinal bias structure. The CIP sensor typically includes a ferromagnetic free layer, a ferromagnetic pinned layer, a spacer layer located between the ferromagnetic free layer and the ferromagnetic pinned layer, and an anti-ferromagnetic (AFM) layer adjacent to the ferromagnetic pinned layer for pinning the magnetic moment of the ferromagnetic pinned layer. The width along the off-track direction of the in-stack longitudinal bias structure is greater than the track-width of the CIP sensor such that the edge magnetostatic coupling field HD acting on the ferromagnetic free layer from the track-width edges of the longitudinal bias structure is reduced to approximately zero. Typically, the track-width of the CIP sensor is between 0.1 xcexcm and 0.4 xcexcm, and the width of the in-stack longitudinal bias structure is greater than 0.5 xcexcm.
The in-stack longitudinal bias structure preferably includes a ferromagnetic bias layer adjacent to the electrically insulating layer and an AFM bias layer. The longitudinal stabilization is achieved by an interlayer magnetostatic coupling (HF) acting on the free layer from the ferromagnetic bias layer across the electrically insulating layer.
In a preferred configuration of the first embodiment, the MR sensing head includes a CIP sensor with the ferromagnetic free layer on the top. The MR sensing head also includes abutted leads located on both sides of the CIP sensor. In this case, the electrically insulating layer includes a first insulating portion located on top of the CIP sensor and second insulating portions located on top of the abutted leads. The first insulating portion is thinner than the second insulating portion. Typically, the thickness of the first insulating portion is between 2 xc3x85 and 100 xc3x85, and the thickness of the second insulating portion is between 30 xc3x85 and 600 xc3x85. The MR sensing head further includes a bottom gap between a bottom shield and the AFM layer of the CIP sensor and a top gap located on top of the in-stack longitudinal bias structure. Since the second insulating portions are thick, these portions can serves as part of the top gap, therefore, the thickness of the top gap can be reduced significantly or eliminated. The thickness of the second gap is typically between zero and 300 xc3x85.
Alternatively, the MR sensing head can include a CIP sensor with the ferromagnetic free layer on the bottom. The MR sensing head further includes abutted leads located on both sides of the CIP sensor. Alternatively, the MR sensing head can include overlaid leads.
In the present invention, the ferromagnetic free layer of the CIP sensor is electrically isolated from the longitudinal bias structure, and the leads that are attached to the CIP sensor do not make electrical contact to the longitudinal bias structure. As a result, the sense current shunting by the longitudinal bias structure is negligible.
In a second embodiment, the MR sensing head of the first embodiment is incorporated into a disk drive system. A disk drive system includes a magnetic recording disk connected to a motor and a MR sensing head connected to an actuator. The motor spins the magnetic recording disk with respect to the MR sensing head, and the actuator positions the MR sensing head relative to the magnetic recording disk.